The common theme of the 3 sections of this proposal is the metabolism of ketone bodies. In the first section, we describe our ongoing research on the potential of R- and S-1, 3-butanediol as parenteral nutrients. We emphasize the interest in S-1, 3- butanediol as a nutrient in diabetes. The metabolism of the 2 enantiomers and of their corresponding 3-hydroxyacids will be studied in perfused organs and in vivo. In the second section, we build on our recent finding that acetone is converted to acetate in the liver. We propose investigations aimed at quantitating the metabolism of acetone via two- and three-carbon pathways. In the third section we propose to investigate the artifact of pseudo-ketogenesis in peripheral tissues. Pseudo-ketogenesis is a process which dilutes the specific activities of plasma acetoacetate and R-3-hydroxy-butyrate, by label exchange via the reversal of the reaction catalyzed by 3-oxoacid-CoA transferase. This artifact leads to overestimations of the rate of ketogenesis measured in vivo by isotope dilution techniques.